I wish I had good answers, but we'll have to settle for what I think. (grin) I don't see the advantage of fighting Whyte now. Though AJ can, and should, win, it's not what I'd pick for him as a tune-up. Whyte can fight, and has the ability to score not just the upset, but to inflict both mental and physical damage in doing so. In my opinion, even if AJ wins, there is a risk of damage.
Now, I think AJ is a very good boxer-puncher. I had supported Tim Witherspoon's attempts to train him after both of AJ's first two loses. It has less to do with phyical conditioning than mental preparation. I know Tim well enough to know he could do that better than the others around AJ. And that's no knock on them. It's a matter of Tim being better for the job, at least in my opinion. And I base that on a number of conversations with Tim about this -- the man has the persoal ring experience, as well as dealing with promoters and fans who love you when you are winning, but not as much after a loss.
I am sure Tim would have advised AJ to fight a less dangerous opponent, not in the top ten. Possibly followed by a top ten guy, then roll the dice with Wilder. Again, just my opinion, but if AJ beats Whyte, then fights Wilder, he will get counted out in about four rounds. With two fights to build him up, the odds would be even.
Sorry to babble on so long! Ask me great questions about boxing, and I can't shut up!